Simultaneous reinforcing and toughening: New nanocomposites of waterborne polyurethane filled with low loading level of starch nanocrystals

New nanocomposites of waterborne polyurethane (WPU) as a matrix were prepared by filling low loading of starch nanocrystals (StNs) as a nano-phase. It is worth noting that the resultant StN/WPU nanocomposites showed significant enhancements in strength, elongation and Youngʹs modulus. Herein, the key role of StN in simultaneous reinforcing and toughening was disclosed, namely active surface and rigidity facilitated forming the interface of transferring stress and contributed to enduring stress, respectively. The preserving of original structure and interaction in WPU matrix was also the essential guarantee of improving mechanical performances. As the StN loading increased, the self-aggregation of StNs caused size expansion of nano-phase along with the increase of number, and hence they decreased the mechanical performances. Furthermore, it was verified that chemical grafting onto the StN surface didnʹt favor enhancing the strength and elongation, due to inhibiting the formation of physical interaction and increasing network density in nanocomposites.